code: def test_ablation_flip_required_field(self):
      ex = {"sentence": "terrible"}
      self.classification_config[ablation_flip.NUM_EXAMPLES_KEY] = 1
      self.classification_config[ablation_flip.FIELDS_TO_ABLATE_KEY] = [
          "sentence"
      ]
      self.assertEmpty(
          self.ablation_flip.generate(
              ex,
              self.classification_model,
              None,
              self.classification_config,
          )
      )
      self.assertLen(
          self.ablation_flip.generate(
              ex,
              self.classification_model_non_required_field,
              None,
              self.classification_config,
          ),
          1,
      )
  
imports: from collections.abc import Iterable, Iterator
  from absl.testing import absltest
  from lit_nlp.api import types
  from lit_nlp.components import ablation_flip
  from lit_nlp.examples.models import glue_models
  import numpy
  from lit_nlp.lib import file_cache
label_desc: Use image node_id 13 for calling the ModelBasedAblationFlipTest obj's underlying member method code with example usage: obj.test_ablation_flip_required_field() without return types